The present invention relates to a shield case for an electronic equipment, such as a receiver, an electronic tuner, and amplifier and so on, which is composed of a plurality of thin metal plates assembled to one another in a box-like shape, having an interior in which circuit boards carrying thereon electronic elements, integrated circuit elements, etc., electronic components and so on are contained.
Generally, in the electronic equipment such as the receiver, the electronic tuner, the amplifier and so on, the circuit boards carrying thereon the electronic elements, the integrated circuit elements, etc., the electronic components and so on are contained in a shield case which is constructed by assembling thin metal plates. The electronic equipment is so constructed that influences of electromagnetic wave noises from outside and occurring inside may be restrained, and mechanical protection can be obtained by the shield case.
As shown in FIG. 5, a related shield case 100 is composed of constituent plates such as a front plate 101, side plates 102, a top plate 104, and a bottom plate (not shown) which are assembled to one another into a box-like shape. In the related shield case 100, the top plate 104 is assembled, after the circuit boards, the electronic components and so on have been received in a state where the top plate 104 is open.
Each of the side plates 102 is integrally provided with a stopper projection 105 by a stamping process or the like at a position adjacent to an upper edge of its outer face in a projecting manner. Similarly, the rear plate 103 is integrally provided with a click projection 106 in a semispherical shape at a position adjacent to an upper edge of its outer face in a projecting manner.
The top plate 104 is integrally provided with side face holding pieces 107 and a rear face holding piece 108 which are respectively bent downward substantially at the right angle along both side edges and a rear face side edge thereof. Each of the side face holding pieces 107 is divided into a plurality of strips by a plurality of slits 109 which open at its lower end edge. As shown in FIG. 6, a lower end portion of the side face holding piece 107 is bent inwardly in a substantially V-shape to form a holding projection 110.
As shown in FIG. 5, the side face holding piece 107 is provided with a guide groove 111 which opens wide in a vertical direction at a position corresponding to the stopper projection 105 of the side plate 102. An open edge 112 at a forward side of the guide groove 111 consists of a slanted edge portion 112a whose open width becomes gradually larger toward the forward side and a vertical edge portion 112b continuing from the slanted edge portion 112a. 
The rear face holding piece 108 is also divided into a plurality of strips by a plurality of slits which open at its lower end edge, although not shown in the drawing, and as shown in FIG. 5, a lower end portion of the rear face holding piece 108 is bent inwardly in a substantially V-shape to form a holding projection 113.
The top plate 104 which has been constructed as described above is assembled to the side plates 102 and the rear plate 103 so as to cover these plates. The holding projection 113 of the rear face holding piece 108 is adapted to climb over the click projection 106 and elastically contact with an outer face of the rear plate 103 thereby to lock the top plate 104. Moreover, when the holding projection 113 of the rear face holding piece 108 climbs over the click projection 106, the entire top plate 104 moves backward to bring the stopper projection 105 into alignment with the guide groove 111 and allows the stopper projection 105 to enter into the guide groove 111. After the holding projection 113 has climbed over the click projection 106, the entire top plate 104 moves forward thereby to bring the stopper projection 105 into contact with the vertical edge portion 112b of the guide groove 111.
The holding projections 110 of the side face holding pieces 107 and the holding projection 113 of the side face holding piece 108 are respectively assembled to the outer faces of the side plates 102 and the rear plate 103 in elastic contact. By locking the holding projection 113 of the rear face holding piece 108 with the click projection 106, the top plate 104 is retained. The top plate 104 is so constructed as to be retained even in such a shield case as having no holding piece at its forward side, because the stopper projection 105 is abutted against the vertical edge portion 112b of the guide groove 111 of the side face holding piece 107 by elastic force of the rear face holding piece 108.
Accordingly, the shield case 100 is so constructed that the constituent members can be assembled to one another by an extremely simple way without employing any fastening means such as screws, welding, deposition, etc. Thus, influence of electromagnetic wave noise can be restrained and mechanical protection for the circuit boards and the electronic components contained therein can be obtained by the shield case 100.
As described, in the related shield case 100 which cannot be provided with a holding piece at its forward side, the stopper projection 105 is abutted against the vertical edge portion 112b of the guide groove 111 of the side face holding piece 107, and the rear face holding piece 108 is locked by the click projection 106 under the elastic forces of the side face holding pieces 107 and the rear face holding piece 108, thereby maintaining the top plate 104 in the assembled state to the side plates 102 and the rear plate 103. The related shield case 100 has such a characteristic that it is flexible in a direction of its thickness, since the holding pieces are provided only at the rear face and the side faces of the top plate 104, and the shield case 100 is formed of thin metal plates.
Therefore, in the case where the shield case 100 has been subjected to a serious impact such as falling down, or a pressure has been applied to the top plate 104, a phenomenon of deformation or flexure occurs in the top plate 104 or the other constituent members in a direction of their thickness. This will force the side face holding pieces 107 and the rear face holding piece 108 to be opened outward, and holding forces for the side plates 102 and the rear plate 103 will be lost. As a result, there may arise a problem that the top plate 104 is disengaged or displaced, and a reliable shield performance cannot be obtained.
It has been considered that the constituent members may be formed of thick metal plates, for example. However, this will lead to a problem that an overall cost will be increased because cost for material, changes in manufacturing steps of the components and in control steps, etc. are required. There will be a further problem that the shield case 100 may become larger in size and heavier in weight by employing such a countermeasure.
In view of the above, it is therefore an object of the present invention to provide a shield case for an electronic equipment in which the top plate is prevented from being detached, even in the case where an impact has been applied, and the shielding performance can be reliably maintained.
In order to achieve the above object, according to the invention, there is provided a shield case for housing an electronic equipment therein, comprising:
a plurality of metal plates including a top plate, a bottom plate, a front plate, a rear plate, a pair of side plates, which are assembled to one another in a box-like shape;
a projection, formed on an outer face of the rear plate;
a stopper projection, formed on an outer face of each side plate;
a rear face holding piece, downwardly extending from a rear edge of the top plate, the rear face holding piece formed with a holding member at a lower end portion thereof, the holding member elastically abutting on the outer face of the rear plate, after climbing over the projection; and
side face holding pieces, downwardly extending from side edges of the top plate, each side face holding piece formed with a notched portion at a lower end portion thereof, the notched portion including:
a guide groove for receiving the stopper projection and moving the top plate forward while the holding member climbs over the projection, and
an engagement groove extending forward from an upper end of the guide groove, for engaging with the stopper projection in accordance with the rearward movement of the top plate when the holding member abuts on the outer face of the rear plate after climbing over the projection.
Here, a width of the engagement groove is wider than a vertical width of the stopper projection, and a length of the engagement groove is shorter than a horizontal width of the stopper projection. A distance between a front end of the engagement groove and the rear face holding piece is longer than a distance between a rear edge of the side plate and a front end of the stopper projection.
In this configuration, the top plate assembled to the side plates and the rear plate is retained at its backward side by locking the rear face holding piece by the projection, and at the same time, retained at its side parts by the stopper projections engaged in the engagement grooves to lock the side face holding pieces. Accordingly, even though flexure or the like may occur in the top plate by an impact of dropping, etc. or a pressure is applied to the shield case, the stopper projections are retained in the engagement grooves. Therefore, a dropout of the top plate can be reliably prevented, because elastic forces of the side face holding pieces and the rear face holding piece are effectively exerted on the side plates and the rear plate.